1. Field of the Invention
The invention relates to screw presses and is particularly applicable to screw presses having a flywheel continuously rotatable in one direction and a pneumatically actuated coupling between the flywheel and the screw, the coupling having a pressure chamber supplied by way of a one-way valve and dischargeable by means of a mass which, under idling or inertial action moves axially of the screw, the resulting axial movement opening the discharge duct of the pressure chamber of the coupling.
2. Description Of The Prior Art
Such a screw press is known, German Auslegeschrift No. 21 10 044, FIG. 6), in which the compressed air is supplied to the pressure chamber by way of a central passage, controlled by a one-way valve, which is connected to the pressure chamber by branch pipes. In addition, the branch pipes are connected to outlets which open out at a face of the coupling, upon which is also disposed the inertially movable mass. This mass is a ring, which is supported on the screw by a non-reversible tooth formation and which in addition, is biased in the axial direction by a spring. At the end of a working stroke, the rotation of the screw is arrested, while the ring rotates further due to its inertia. On account of the interposed screw, the ring lifts, against the action of the spring, away from the outlet of the pressure chamber, so that the compressed air present in the pressure chamber can flow through the outlet.
It has been found that, at the end of the working stroke, the ring does not lift from the outlet quickly enough to bring about an immediate discharge of the pressure chamber and therewith a prompt release of the coupling. Rather, the aperture is gradually uncovered by the ring and accordingly, the compressed air can only flow or stream slowly out of the pressure chamber. Hence, the coupling is slowly released and still drags after the end of the working stroke. That leads to undesirable wear of the coupling and to excessive loading of the press after the end of the working stroke. Furthermore, the operation of the control mechanism for the coupling is dependent upon the speed of rotation of the screw, which during the working stroke drives the ring and in that way determines its inertial idling action relative to the spring force.
In addition, the operation of the known screw press in the case of an emergency stop also leaves something to be desired. For practical embodiments one can install in the central passage for the compressed air supply a multi-way valve or the like, which is operated on the occasion of an emergency stop and makes possible discharging of the pressure chamber. There too, one achieves only a comparatively slow discharge of the pressure chamber, because the available cross-section of the central passage for the pressure fluid supply is restricted. Generally, it is known to effect a quick pressure discharge through a balanced valve.